<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="text"><button>点击</button>
    <div></div>
    <script>
        //trim方法去除字符串两侧空格
        var str = '   an dy   ';
        console.log(str);
        var str1 = str.trim();
        console.log(str1);
        var input = document.querySelector('input');
        var btn = document.querySelector('button');
        var div = document.querySelector('div');
        btn.onclick = function(){

            var str = input.value.trim();
            if(str === '')
            {
                alert('请输入内容');
            }else{
                console.log(str);
                console.log(str.length);
                div.innerHTML = str;
            }
        }
    </script>
</body>
</html>